Method for manufacturing secondary battery

ABSTRACT

Provided is a method for manufacturing a secondary battery including a stacked electrode body including a plurality of positive electrode plates ( 1 ) and a plurality of negative electrode plates, the positive electrode plates ( 1 ) each having a positive electrode active material layer ( 1   b ) formed on a positive electrode substrate ( 1   a ), a positive electrode substrate exposed portion where the positive electrode active material layer ( 1   b ) is not formed on the positive electrode substrate ( 1   a ) being provided as a positive electrode tab portion ( 1   e ) at the end of the positive electrode plate ( 1 ). The method includes a cutout forming step of providing a cutout in a region at the base of the positive electrode plate ( 1 ) where the active material layer ( 1   b ) is formed, and a compressing step of compressing the positive electrode active material layer ( 1   b ) after the cutout forming step.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a secondarybattery.

BACKGROUND ART

Secondary batteries such as nonaqueous electrolyte secondary batteriesare used in power sources for driving electric vehicles (EV), hybridelectric vehicles (HEV, PHEV), and the like.

These secondary batteries include a positive electrode plate and anegative electrode plate in which an active material layer containing anactive material is formed on the surface of a substrate composed of ametal foil. Further increase in energy density is required for secondarybatteries used for electric vehicles (EV), hybrid electric vehicles(HEV, PHEV) and the like. As a method for increasing the energy densityof the secondary battery, it is conceivable to further increase thepacking density of the active material layer. Thereby, it is possible toincrease the amount of the active material contained in the battery caseand to improve the energy density. As a method for further increasingthe packing density of the active material layer, for example, it isconceivable to further increase the packing density of the activematerial layer by compressing with a stronger force when the activematerial layer is compressed by roll press or the like after the activematerial layer is provided on the substrate.

However, when the active material layer formed on the substrate iscompressed with a stronger force, not only the active material layer butalso the substrate having the active material layer formed on itssurface is strongly compressed, so that the substrate is rolled. Here,when a substrate exposed portion having no active material layer famedthereon is present at the end portion of the electrode plate, thesubstrate exposed portion has a smaller thickness than the portionhaving the active material layer famed thereon, so that the load of thecompression treatment is not applied to the substrate exposed portion.Therefore, when the electrode plate is subjected to rolling treatment,the portion of the substrate where the active material layer is formedis rolled, but the substrate exposed portion is not rolled. Therefore,there is a difference in length between the portion of the substratewhere the active material layer is famed and the substrate exposedportion. There is a problem that wrinkles are generated in the substrateand the electrode plate is curved due to the generated difference inlength.

In order to solve such a problem, the following PTL 1 proposes atechnique of roll-pressing the electrode plate after elongating thesubstrate exposed portion of the electrode plate.

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 5390721

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a highly reliableelectrode plate and a secondary battery using the same.

Solution to Problem

In an aspect of the present invention, there is provided a method formanufacturing a secondary battery including a stacked electrode bodyincluding a plurality of first electrode plates and a plurality ofsecond electrode plates, the first electrode plates each having asubstrate, an active material layer famed on the substrate, and a tabportion composed of a substrate exposed portion where the activematerial layer is not formed. The method includes a cutout forming stepof providing at least one cutout in a region of each first electrodeplate that is at the base of the tab portion and in which the activematerial layer is formed, and a compressing step of compressing theactive material layer after the cutout forming step.

The above-described configuration makes it possible to provide a highlyreliable secondary battery.

The following procedure is conceivable as a manufacturing procedure ofan electrode plate in which an active material layer is famed on bothsides of a substrate and a substrate exposed portion as a tab portion isprovided at an end.

(1) An active material layer is formed on both sides of a belt-likesubstrate such that a substrate exposed portion is famed along thelongitudinal direction of the substrate.

(2) The substrate exposed portion is cut into a predetermined shape toform a tab portion.

(3) The belt-like electrode plate having the tab portion famed thereonis pressed to compress the active material layer.

The inventors have found that, in the case of manufacturing an electrodeplate by such a procedure, if the pressing pressure in the pressingtreatment of the electrode plate is increased in order to make thepacking density of the active material layer higher, a crack extendingin the oblique direction may be generated in the base portion of the tabportion. The cause of such a problem is considered as follows.

It has been considered that, in general, when the electrode plate ispressed after the substrate exposed portion is cut into a predeterminedshape to form the tab portion, the electrode plate is unlikely to bewrinkled, curved, or cracked even if a difference in length occursbetween the portion of the substrate where the active material layer isformed and the substrate exposed portion in the pressing treatment. Thatis, since the substrate exposed portion is cut at a constant interval,even if a difference in length occurs between the portion of thesubstrate where the active material layer is formed and the substrateexposed portion due to the pressing treatment, the strain is released atthe position where the substrate exposed portion is cut, so that theelectrode plate is unlikely to be wrinkled, curved, or cracked.

However, in the course of development by the inventors, a crack wassometimes generated at the base of the tab portion even in the casewhere the electrode plate was pressed after the substrate exposedportion was cut into a predetermined shape to form the tab portion. Theinventors have found that such a problem appears significantly when thepacking density of the active material layer after the compressiontreatment is 3.58 g/cm³ or more and the width of the tab portion is 10mm or more.

Although it is possible to suppress the occurrence of a crack at thebase of the tab portion to some extent by making the width of the tabportion smaller than 10 mm, it is not preferable because the electricresistance value may increase if the width of the tab portion is madetoo small.

The inventors have found that the occurrence of a crack at the base ofthe tab portion of the electrode body can be effectively suppressed byperforming a treatment of compressing the active material layer afterthe cutout is provided in a region of the electrode plate that is at thebase of the tab portion and in which the active material layer is famed.

Advantageous Effects of Invention

According to the present invention, a secondary battery having higherreliability can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a positive electrode plate before cutting.

FIG. 2 is a sectional view of the positive electrode plate taken alongline II-II of FIG. 1.

FIG. 3 is a plan view of the positive electrode plate after forming tabportions.

FIG. 4 is an enlarged view of the vicinity of the tab portion in FIG. 3.

FIG. 5 is a diagram showing the step of compressing the positiveelectrode plate.

FIG. 6 is a plan view of a positive electrode plate after cutting and anegative electrode plate after cutting.

FIG. 7 is a sectional view of a prismatic secondary battery.

FIG. 8 is an enlarged view of the vicinity of a tab portion in apositive electrode plate according to Modification 1.

FIG. 9 is an enlarged view of the vicinity of a tab portion in apositive electrode plate according to Modification 2.

DESCRIPTION OF EMBODIMENTS

An embodiment according to the present invention will be described as anexample of a method for manufacturing a nonaqueous electrolyte secondarybattery. The present invention is not limited to the followingembodiment.

First, a method for manufacturing a positive electrode plate will bedescribed.

[Preparation of Positive Electrode Active Material Layer Slurry]

Lithium nickel cobalt manganese complex oxide as a positive electrodeactive material, polyvinylidene fluoride (PVdF) as a binder, carbonmaterial as a conductive agent, and N-methyl-2-pyrrolidone (NMP) as adispersion medium are kneaded such that the mass ratio of lithium nickelcobalt manganese composite oxide:PVdF:carbon material is 97.5:1:1.5 toprepare a positive electrode active material layer slurry. The contentof the positive electrode active material in the positive electrodeactive material layer is preferably 95% by mass or more, and preferably99% by mass or less. The content of the binder in the positive electrodeactive material layer is preferably 0.5% by mass or more, and preferably3% by mass or less.

[Preparation of Protective Layer Slurry]

Alumina powder, graphite as a conductive agent, polyvinylidene fluoride(PVdF) as a binder, and N-methyl-2-pyrrolidone (NMP) as a dispersionmedium are kneaded such that the mass ratio of aluminapowder:graphite:PVdF is 83:3:14 to prepare a protective layer slurry.The content of the binder in the protective layer is preferably 5% bymass or more, more preferably 8% by mass or more, and still morepreferably 10% by mass or more. The protective layer may be composedonly of a binder, but preferably contains ceramic particles such asalumina, zirconia, titania and silica. It is preferable that theprotective layer contain no positive electrode active material. Evenwhen the protective layer contains the positive electrode activematerial, the content thereof is preferably 5% by mass or less, morepreferably 1% by mass or less.

[Active Material Layer Forming Step and Protective Layer Forming Step]

The positive electrode active material layer slurry and the protectivelayer slurry prepared by the above method are applied to both sides ofan aluminum foil having a thickness of 15 μm as a positive electrodesubstrate by a die coater. At this time, the positive electrode activematerial layer slurry is applied to the center in the width direction ofthe positive electrode substrate, and the protective layer slurry isapplied to both ends in the width direction of the region where thepositive electrode active material layer slurry is applied. The positiveelectrode active material layer slurry and the protective layer slurrycan be combined in the vicinity of the discharge port inside the diehead of one die coater, and the positive electrode active material layerslurry and the protective layer slurry can be simultaneously appliedonto the positive electrode substrate. However, it is not necessary tosimultaneously apply the positive electrode active material layer slurryand the protective layer slurry to the positive electrode substrate.

The positive electrode substrate coated with the positive electrodeactive material layer slurry and the protective layer slurry is dried toremove NMP in the slurries. Thus, a positive electrode active materiallayer and a protective layer are famed.

FIG. 1 is a plan view of a positive electrode plate 1 before thecompression treatment fabricated by the above method. FIG. 2 is asectional view of the positive electrode plate 1 taken along line II-IIof FIG. 1. As shown in FIGS. 1 and 2, a positive electrode activematerial layer 1 b is formed on both sides of a positive electrodesubstrate 1 a along the longitudinal direction of the positive electrodesubstrate 1 a. A protective layer 1 c is formed at both ends in thewidth direction of a region of the positive electrode substrate 1 awhere the positive electrode active material layer 1 b is formed. Atboth ends in the width direction of the positive electrode plate 1, apositive electrode substrate exposed portion 1 d is formed along thelongitudinal direction of the positive electrode plate 1. Here, thethickness of the positive electrode active material layer 1 b is largerthan the thickness of the protective layer 1 c.

The positive electrode plate 1 shown in FIGS. 1 and 2 is cut along lineC-C in FIG. 2.

[Tab Portion Forming Step and Cutout Forming Step]

In the positive electrode plate 1 shown in FIGS. 1 and 2, an energy beamsuch as a laser beam is irradiated to the positive electrode substrateexposed portion 1 d, thereby cutting the positive electrode substrateexposed portion 1 d into a predetermined shape to form positiveelectrode tab portions 1 e. At this time, at the same time as formationof the tab portion, an energy beam such as a laser beam is irradiated toa region at the base of the tab portion where the positive electrodeactive material layer 1 b and the protective layer 1 c are provided,thereby providing cutouts 1 f.

FIG. 3 is a diagram showing a positive electrode plate 1 provided withpositive electrode tab portions 1 e and cutouts 1 f. As shown in FIG. 3,the positive electrode tab portions 1 e are formed at an end of thepositive electrode plate 1. The positive electrode tab portions 1 e areprovided so as to protrude from a region of the positive electrodesubstrate 1 a where the positive electrode active material layer 1 b isformed.

The formation of the tab portions and the formation of the cutouts maybe performed separately. The formation of the tab portions and theformation of the cutouts may be performed by different methods. Forexample, the formation of the tab portions may be performed by presspunching, and then the formation of the cutouts may be performed byirradiation with an energy beam.

[Compressing Step]

As shown in FIG. 5, a positive electrode plate 1 provided with positiveelectrode tab portions 1 e and cutouts 1 f is passed between a pair ofpress rollers 30, and the positive electrode active material layer 1 bis compressed. Thereby, the packing density of the positive electrodeactive material layer 1 b is increased. The packing density of thepositive electrode active material layer 1 b is preferably set to 3.58g/cm³ or more.

Thereafter, the positive electrode plate 1 subjected to compressiontreatment is cut into a predetermined shape, and a positive electrodeplate 1 shown in (a) of FIG. 6 is completed. Broken lines in FIG. 3indicate positions at which the positive electrode plate 1 is cut.

When a positive electrode plate 1 is fabricated by the above method,cutouts 1 f are provided in a region of the positive electrode plate 1that is at the base of the positive electrode tab portion 1 e and inwhich the positive electrode active material layer 1 b is formed, andthen the positive electrode active material layer 1 b is compressed.Therefore, a crack can be prevented from being generated at the base ofthe positive electrode tab portion 1 e of the positive electrode plate 1due to the compression treatment. The reason why such an effect can beobtained is considered as follows.

The region of the positive electrode substrate in which the positiveelectrode active material layer is formed is rolled by the rollingtreatment. The tab portion, where the positive electrode active materiallayer is not formed, has a smaller thickness than the portion where thepositive electrode active material layer is present. Therefore, the tabportion is not rolled in the compression treatment. In this case, in thepositive electrode substrate on which the positive electrode activematerial layer is formed, a portion adjacent to the tab portion is fixedto the tab portion, which is not rolled. On the other hand, a portionthat is slightly distant from the tab portion is rolled and is pulled inthe left-right direction (in the longitudinal direction of the positiveelectrode substrate).

In the positive electrode plate 1, cutouts 1 f are provided in theregion at the base of the positive electrode tab portion 1 e where thepositive electrode active material layer 1 b is formed. Therefore, thestarting point of a crack is removed, and a crack can be prevented frombeing generated.

As shown in FIG. 4, the cutout 1 f is preferably famed in a regionincluding an intersection of an extension line of a side edge 1 x of thepositive electrode tab portion 1 e of the positive electrode plate 1 andan extension line of the upper edge 1 y of the region of the positiveelectrode plate 1 where the positive electrode active material layer 1 bis formed (the edge from which the positive electrode tab portion 1protrudes). Thereby, it is possible to more effectively prevent a crackfrom being generated at the base of the positive electrode tab portion 1e of the positive electrode plate 1 due to the compression treatment.

As shown in FIG. 4, the cutouts 1 f are preferably formed in the regionwhere the positive electrode active material layer 1 b is formed. Thus,since the edges of the cutouts 1 f are reinforced by the positiveelectrode active material layer 1 b, it is possible to effectivelyprevent the positive electrode plate 1 from cracking or breaking fromthe cutouts 1 f after the positive electrode plate 1 is fabricated.Further, since the first edge E1 of the cutout 1 f is covered with thepositive electrode active material layer 1 b, it is possible to reliablyprevent the first edge E1 from penetrating the separator and coming intocontact with the negative electrode plate 2.

It is preferable that, as shown in FIG. 4, cutouts 1 f be provided onboth sides of the base of the positive electrode tab portion 1 e, and apositive electrode active material layer 1 b be formed on a straightline connecting the cutouts 1 f at the shortest distance. Thus, sincethe portion connecting the two cutouts 1 f at the shortest distance isreinforced by the positive electrode active material layer 1 b, it ispossible to effectively prevent the positive electrode plate 1 fromcracking or breaking from the cutouts 1 f after the positive electrodeplate 1 is fabricated.

As shown in FIG. 4, the cutouts 1 f are preferably formed in the regionwhere the protective layer 1 c is formed. Thus, since the edges of thecutouts 1 f are reinforced by the protective layer 1 c, it is possibleto effectively prevent the positive electrode plate 1 from cracking orbreaking from the cutouts 1 f after the positive electrode plate 1 isfabricated. Further, since the second edge E2 of the cutout 1 f iscovered with the protective layer 1 c, it is possible to reliablyprevent the second edge E2 from penetrating the separator and cominginto contact with the negative electrode plate 2.

It is preferable that, in the protruding direction of the positiveelectrode tab portion 1 e, the first edge E2 be located closer to thetip of the positive electrode tab portion 1 e than the first edge E1,the second edge E2 be covered with the protective layer 1 c, and theconductivity of the protective layer 1 c be lower than the conductivityof the positive electrode active material layer 1 b. Since the secondedge E2 penetrates the separator more easily than the first edge E1, thelayer formed on the second edge E2 is the protective layer 1 c withlower conductivity, which improves safety.

It is preferable that, as shown in FIG. 4, the entire edges of thecutouts 1 f be disposed in the region where the positive electrodeactive material layer 1 b is formed or the region where the protectivelayer 1 c is formed. Thereby, it is possible to effectively preventcracks from being generated from the edges of the cutouts 1 f.

The cutouts 1 f are preferably formed by irradiation with an energy beamsuch as a laser beam. Thereby, the edges of the cutouts 1 f areprevented from becoming sharp and have a more rounded shape, andtherefore it is possible to more reliably prevent cracks from beinggenerated therefrom. It is preferable that, in the positive electrodesubstrate 1 a, the thickness of the edges of the cutouts 1 f is largerthan that of the other region.

Although the shape of the cutouts 1 f is not particularly limited, thecutouts 1 f preferably have a circular arc shape. Thereby, it ispossible to prevent cracks from being generated therefrom. For example,each cutout is preferably a part of a circle having a diameter of 1 to10 mm.

As shown in FIG. 4, in the width direction of the positive electrode tabportion 1 e, the end of each cutout 1 f closer to the center of thepositive electrode tab portion 1 e is preferably located closer to thecenter of the positive electrode tab portion 1 e than the end in thewidth direction of the positive electrode tab portion 1 e. Thereby, itis possible to more effectively prevent the electrode plate from tearingwhen the positive electrode plate 1 is pressed.

The width W1 of the positive electrode tab portion 1 e is preferably 12mm to 30 mm. The smaller the width W1 of the positive electrode tabportion 1 e, the less likely the crack generated during the step ofcompressing the positive electrode plate 1 is to be generated. However,when the width W1 of the positive electrode tab portion 1 is small, theelectric resistance increases, which is not preferable. According to thepresent invention, it is possible to provide a positive electrode plate1 that suppresses an increase in electric resistance and is less likelyto crack.

As shown in FIG. 4, it is preferable that cutouts 1 f be provided onboth sides of the base of the positive electrode tab portion 1 e. Inthis case, the width W2 of the portion connecting the pair of cutouts 1f at the shortest distance is preferably ½ to ⅘ of the width W1 of thetab portion. When the width W2 of the portion connecting the cutouts atthe shortest distance is small, it is not preferable because theresistance value increases and there is a possibility of fusion.However, it is preferable that the portion connecting the cutouts at theshortest distance be a portion where the active material layer isformed, because the fusion can be suppressed.

It is preferable that only one positive electrode tab portion 1 e beprovided in one positive electrode plate 1. Since it is preferable thatthe electrode body be fabricated while the region of the positiveelectrode plate 1 where the positive electrode active material layer 1 bis famed is kept flat, it is preferable to use for a battery including astacked electrode body.

It is preferable that each cutout 1 f be a part of a circle, and thecenter of the circle be located at the portion where the positiveelectrode active material layer 1 b is famed (that is, the center of thecircle be located below an extension line of the upper edge 1 y of theregion where the positive electrode active material layer 1 b isformed).

[Method for Manufacturing Prismatic Secondary Battery]

A method for manufacturing a prismatic second battery 20 using thepositive electrode plate 1 fabricated by the above method will bedescribed.

[Fabrication of Negative Electrode Plate]

A negative electrode active material layer slurry containing graphite asa negative electrode active material, styrene butadiene rubber (SBR) asa binder, carboxymethyl cellulose (CMC) as a thickener, and water isprepared. This negative electrode active material layer slurry isapplied to both sides of a rectangular copper foil having a thickness of8 μm as a negative electrode substrate. Then, by drying this, water inthe negative electrode active material layer slurry is removed, and anegative electrode active material layer is famed on the negativesubstrate. Thereafter, the negative electrode active material layer iscompressed so as to have a predetermined thickness. The negativeelectrode plate thus obtained is cut into a predetermined shape, and anegative electrode plate shown in (b) of FIG. 6 is made.

[Fabrication of Electrode Body]

A plurality of positive electrode plates 1 and a plurality of negativeelectrode plates 2 made by the above method are stacked with polyolefinseparators therebetween to fabricate a stacked electrode body 3. Here,each of the positive electrode plates 1 and the negative electrodeplates 2 is not curved, and has a flat shape. In the stacked electrodebody 3, stacked positive electrode tab portions 1 e and stacked negativeelectrode tab portions 2 c protrude from one end thereof. In the stackedelectrode body 3, the shape of the separators is not particularlylimited. A plurality of flat separators may be used. A plurality ofbag-shaped separators in which one of the electrode plates is disposedmay be used. Alternatively, a separator may be folded zigzag.

[Assembling of Sealing Body]

As shown in FIG. 7, a sealing plate 5 has a positive electrode terminalmounting hole 5 a and a negative electrode terminal mounting hole 5 b.An insulating member 10 and a positive electrode current collector 6 aredisposed around the positive electrode terminal mounting hole 5 a on theinner side of the battery. An insulating member 11 is disposed aroundthe positive electrode terminal mounting hole 5 a on the outer side ofthe battery. Then, a positive electrode terminal 7 is inserted from theouter side of the battery into a through-hole provided in each of theinsulating member 11, the insulating member 10 and the positiveelectrode current collector 6, and the tip of the positive electrodeterminal 7 is fixed by caulking onto the positive electrode currentcollector 6. The caulking portion of the positive electrode terminal 7is preferably welded to the positive electrode current collector 6.

An insulating member 12 and a negative electrode current collector 8 aredisposed around the negative electrode terminal mounting hole 5 b on theinner side of the battery. An insulating member 13 is disposed aroundthe negative electrode terminal mounting hole 5 b on the outer side ofthe battery. Then, a negative electrode terminal 9 is inserted from theouter side of the battery into a through-hole provided in each of theinsulating member 13, the insulating member 12 and the negativeelectrode current collector 8, and the tip of the negative electrodeterminal 9 is fixed by caulking onto the negative electrode currentcollector 8. The caulking portion of the negative electrode terminal 9is preferably welded to the negative electrode current collector 8.

[Connecting Tab Portion and Current Collector]

The stacked positive electrode tab portions 1 e of the stacked electrodebody 3 are connected by welding to the positive electrode currentcollector 6, and the stacked negative electrode tab portions 2 c of thestacked electrode body 3 are connected by welding to the negativeelectrode current collector 8. As the connection by welding, resistancewelding, laser welding, ultrasonic welding, or the like can be used.

[Assembling of Secondary Battery]

The stacked electrode body 3 covered with an insulating sheet 17 isinserted into a bottomed prismatic outer casing 4. Thereafter, the outercasing 4 and the sealing plate 5 are connected by welding to each other,and the opening of the outer casing 4 is sealed. Thereafter, anonaqueous electrolytic solution containing an electrolyte and a solventis injected into the outer casing 4 through an electrolytic solutioninjection hole 15 provided in the sealing plate 5. Thereafter, theelectrolytic solution injection hole 15 is sealed with a sealing plug16.

The sealing plate 5 is provided with a gas discharge valve 14 thatbreaks when the pressure in the battery reaches a predetermined value ormore and discharges the gas in the battery to the outside. A currentinterruption mechanism may be provided in the conductive path betweenthe positive electrode plate 1 and the positive electrode terminal 7 orthe conductive path between the negative electrode plate and thenegative electrode terminal 9. It is preferable that the currentinterrupting mechanism operate to cut off the conductive path when thepressure in the battery reaches a predetermined value or more. Theoperating pressure of the current interrupting mechanism is set lowerthan the operating pressure of the gas discharge valve.

In the above embodiment, cutouts 1 f are provided in the positiveelectrode plate 1, but cutouts may be provided in a portion at the baseof the negative electrode tab portion 2 c of the negative electrodeplate 2 where the negative electrode active material layer 2 b isformed.

Although the protective layer 1 c is provided on the positive electrodeplate 1 in the above embodiment, the protective layer 1 c is notessential and the protective layer 1 c may not be provided.

Next, modifications will be described.

[Modification 1]

FIG. 8 is a plan view of a positive electrode plate 1 according toModification 1. The positive electrode plate 1 according to Modification1 differs only in the formation positions of the cutouts 1 f, and theother configuration and manufacturing procedure are the same as those ofthe positive electrode plate 1 in the above-described embodiment.

The positive electrode plate 1 according to Modification 1 differs fromthe positive electrode plate 1 according to the above embodiment inthat, when each cutout 1 f is considered to be a part of a circle, thecenter of the circle is shifted away from the center of the positiveelectrode tab portion 1 e, and the center of the circle is shifted inthe protruding direction of the tab portion. In the positive electrodeplate 1 according to Modification 1, in the width direction of thepositive electrode tab portion 1 e, the end of each cutout 1 f closer tothe center of the positive electrode tab portion 1 e coincides with theend of the positive electrode tab portion 1 e.

[Modification 2]

FIG. 9 is a plan view of a positive electrode plate 1 according toModification 2. The positive electrode plate 1 according to Modification2 differs only in the formation positions of the cutouts 1 f, and theother configuration and manufacturing procedure are the same as those ofthe positive electrode plate 1 in the above-described embodiment.

In the positive electrode plate 1 according to Modification 2, a cutout1 f is provided only on one side in the width direction of the base ofthe positive electrode tab portion 1 e. In such a case, the cutout 1 fis preferably provided on the upstream side (the side that is pressedfirst) of the positive electrode plate 1 in the rolling treatment. Thecrack generated at the base of the positive electrode tab portion 1 ewhen the positive electrode plate 1 is compressed, tends to be generatedon the upstream side of the positive electrode plate 1 in the rollingtreatment. Therefore, with the configuration of Modification 2, ahigh-quality positive electrode plate 1 can be obtained while minimizingthe decrease in battery capacity.

<Others>

The present invention is applicable to both a positive electrode plateand a negative electrode plate. However, it is particularly effective toapply the present invention to a positive electrode plate. It isparticularly effective to apply the present invention to a positiveelectrode plate having a positive electrode active material layer havinga packing density of 3.58 g/cm³ or more after the compression treatment.

The substrate in the present invention is preferably a non-porous metalfoil. The positive electrode substrate is preferably an aluminum foil oran aluminum alloy foil. The negative electrode substrate is preferably acopper foil or a copper metal foil.

The electrode body in the present invention is preferably a stackedelectrode body including a plurality of flat positive electrode platesand a plurality of flat negative electrode plates. The shape ofseparators disposed between the positive electrode plates and thenegative electrode plates is not particularly limited. Flat separatorscan be disposed between the positive electrode plates and the negativeelectrode plates. Alternatively, the separators may be formed in a bagshape and the positive electrode plates may be disposed therein.Alternatively, a separator may be folded zigzag and the positiveelectrode plates and the negative electrode plate may be disposedtherebetween.

A lithium transition metal composite oxide is preferable as the positiveelectrode active material in the present invention. In particular, alithium transition metal composite oxide containing at least one ofnickel, cobalt and manganese is preferable.

A material capable of absorbing and releasing lithium ions can be usedas the negative electrode active material in the present invention.Materials capable of absorbing and releasing lithium ions include carbonmaterials such as graphite, hardly graphitizable carbon, easilygraphitizable carbon, fibrous carbon, coke and carbon black. Examples ofthe non-carbon material include silicon, tin, and alloys and oxidesmainly containing them. A carbon material and a non-carbon material canbe mixed.

Examples of the binder contained in the active material layer and theprotective layer of the electrode plate include polyvinylidene fluoride(PVDF), polytetrafluoroethylene, polyethylene, polypropylene, aramidresin, polyamide, polyimide, polyamide imide, polyacrylonitrile,polyacrylic acid, poly(methyl acrylate), poly(ethyl acrylate),poly(hexyl acrylate), polymethacrylic acid, poly(methyl methacrylate),poly(ethyl methacrylate), poly(hexyl methacrylate), polyvinyl acetate,polyvinylpyrrolidone, polyether, polyether sulfone,hexafluoropolypropylene, styrene butadiene rubber, carboxymethylcellulose, acrylic rubber, and acrylate binder (ester or salt of acrylicacid). These may be used alone or in combination of two or more. Thebinder contained in the active material layer and the binder containedin the protective layer may be the same or different. The binder ispreferably made of resin.

The mass ratio of the binder contained in the protective layer to theprotective layer is preferably 5% by mass or more, and more preferably10% by mass or more. The mass ratio of the binder contained in theprotective layer to the protective layer is preferably 95% by mass orless. However, the protective layer may be composed only of a binder.However, the protective layer preferably contains at least one ofalumina, zirconia, titania and silica as ceramic particles.

<Other Invention>

A method for manufacturing an electrode plate for a secondary batteryaccording to another invention is a method for manufacturing anelectrode plate for a secondary battery including a substrate composedof a metal foil, an active material layer containing an active materialfamed on the substrate, the substrate on the surface of which the activematerial layer is not formed being provided as a tab portion, aprotective layer containing ceramic particles and a binder being famedon the substrate in a portion that is at the base of the tab portion andadjacent to the active material layer, the method including: a cutoutforming step of providing a cutout in a portion that is at the base ofthe tab portion and in which the active material layer and theprotective layer are formed; and a compressing step of compressing theactive material layer after the cutout forming step.

With the method for manufacturing an electrode body according to theother invention, it is possible to more effectively prevent a crack frombeing generated at the base of the tab portion when the electrode plateis compressed. Since the cutout is formed in a region of the substratewhere the active material layer and the protective layer are famed, theedge of the cutout is reinforced by the active material layer and theprotective layer. Therefore, it is possible to effectively prevent theelectrode plate from cracking from the cutout. In addition, since theedge of the cutout is covered with the active material layer and theprotective layer, it is possible to prevent the edge from penetratingthe separator and coming into contact with the opposing electrode plate.

The electrode plate according to the other invention can be used as atleast one of a positive electrode plate and a negative electrode plate.It is possible to fabricate a rolled electrode body using the electrodeplate according to the other invention, and it is also possible tofabricate a stacked electrode body.

REFERENCE SIGNS LIST

-   -   1 positive electrode plate        -   1 a positive electrode substrate        -   1 b positive electrode active material layer        -   1 c protective layer        -   1 d positive electrode substrate exposed portion        -   1 e positive electrode tab portion        -   1 f cutout    -   negative electrode plate        -   2 b negative electrode active material layer        -   2 c negative electrode tab portion (negative electrode            substrate exposed portion)    -   3 stacked electrode body    -   3 outer casing    -   4 sealing plate        -   5 a positive electrode terminal mounting hole        -   5 b negative electrode terminal mounting hole    -   6 positive electrode current collector    -   7 positive electrode terminal    -   8 negative electrode current collector    -   9 negative electrode terminal    -   10 insulating member    -   11 insulating member    -   12 insulating member    -   13 insulating member    -   14 gas discharge valve    -   15 electrolytic solution injection hole    -   16 sealing plug    -   17 insulating sheet    -   20 prismatic secondary battery    -   30 press roller

The invention claimed is:
 1. A method for manufacturing a secondarybattery including a stacked electrode body including a plurality offirst electrode plates and a plurality of second electrode plates, thefirst electrode plates each having a belt-like substrate, an activematerial layer formed on the belt-like substrate, and a tab portioncomposed of a substrate exposed portion where the active material layeris not formed, wherein the belt-like substrate and the tab portion areformed of a single integral piece of material, the method comprising: anactive material layer formation step of forming the active materiallayer on both sides of the belt-like substrate such that a substrateexposed portion is formed along a longitudinal direction of thebelt-like substrate; a tab portion formation step of cutting thesubstrate exposed portion into a predetermined shape to form the tabportion; a cutout forming step of providing at least one cutout in aperipheral region of each first electrode plate that is located directlyadjacent to a base of the tab portion and in which the active materiallayer is formed, wherein the peripheral region includes at least aportion of the belt-like substrate which is directly adjacent to anddistinct from the tab portion and has the active material layer formedthereon; and a compressing step of compressing the active material layerafter the cutout forming step, wherein a protective layer containingceramic particles and a binder is formed on the tab portion before thecutout forming step, and wherein the at least one cutout is also formedin a region where the protective layer is formed.
 2. The method formanufacturing a secondary battery according to claim 1, wherein thefirst electrode plates are positive electrode plates, and the secondelectrode plates are negative electrode plates, wherein the belt-likesubstrate is an aluminum foil or an aluminum alloy foil, and wherein thepacking density of the active material layer after the compression stepis 3.58 g/cm³ or more.
 3. The method for manufacturing a secondarybattery according to claim 1, wherein, in the cutout forming step, theat least one cutout is provided using an energy beam.
 4. The method formanufacturing a secondary battery according to claim 1, wherein, in thewidth direction of the tab portion, the end of the at least one cutoutcloser to the center of the tab portion is located closer to the centerof the tab portion than the end in the width direction of the tabportion.
 5. The method for manufacturing a secondary battery accordingto claim 1, wherein the at least one cutout comprises two cutouts, and,in the width direction of the tab portion, the two cutouts are providedon both sides of the base of the tab portion.